Cnc controlled buttonhole sewing machine

A buttonhole sewing machine, comprising

• a needle (7) drivable via an arm shaft (4);
• an x-y table (8),
• which is displaceable in an x direction by an x drive (9) and in a y direction by a y drive (10),
• which supports a first and a second work piece clamp (13a, 13b) mounted for displacement relative to each other, and
• which comprises a pneumatically actuated displacement drive (44) for displacement of the work piece clamps (13a, 13b) relative to each other from an initial position of spread by a length of spread (d) into a final position of spread;
• and
• a control unit (62) for control of the drives (9, 10, 44);
• wherein only the first work piece clamp (13b) is displaceable relative to the x-y table (8), and the second work piece clamp (13a) is non-displaceable relative to the x-y table (8);
• and
• wherein means are provided for defining a displacement of the first work piece clamp (13b) relative to the x-y table (8) by a given length of spread (d) in a first direction between a first stop position and a second stop position of the first work piece clamp (13b);
• and
• wherein the control unit (62) stores data for triggering the x drive (9) for a displacement of the x-y table (8) by half the given length of spread (d) in a second direction reversed to the first direction.